The present invention relates to a control apparatus of the type which includes a primary control unit capable of taking variable operative positions and a secondary control unit operable in accordance with the operative positions of the primary control unit, and a method of controlling the operation of such control apparatus.
The control apparatus including the primary control unit and the secondary control unit has been used in the various technical fields. For example, U.S. Pat. No. 4,097,183 discloses a hydraulic system which comprises a primary control unit including wicket gates of a water turbine and a secondary control unit including a bypass valve. In this hydraulic system, the bypass valve is controlled to open or close in an interlocked relation with the wicket gates in order to bypass a stream of water with respect to the turbine in accordance with the opening or closing action of the wicket gates, thereby maintaining total water flow through the penstock constant in each transient state of the wicket gate motion and minimizing the resultant water pressure changes in the penstocks. The system includes signal transmitting means which detects the position of the wicket gates and transmitting the corresponding signal to the bypass valve to control the latter. In this system, it is apparently preferable that the follow-up characteristics of the operation of the bypass valve responsive to the position of the wicket gates can be improved.
As a measure to improve the follow-up characteristics, it is conceivable to control the bypass valve by transmitting thereto a differential signal of the opening and closing motions of the wicket gates in addition to the position signal of the wicket gates.
More practically, it is conceivable to control the bypass valve by a combined signal of the wicket gate responsive signal and a signal responsive to position of the pressure distributor valve for the wicket gates. However, in such practical design, the distributor valve responsive signal does not always represent the desired differential signal of the wicket gates since there are some hydraulical or mechanical restricting means between the wicket gate distributor valve and the wicket gate driving servo-motor.